Pneumatic and hydraulic systems commonly include valves to alternately permit or prevent fluid flow. For example, some valves may be normally open to permit fluid flow through the valves, while other valves may be normally shut to prevent fluid flow through the valves. In some fluid systems, the accurate position of one or more valves may be necessary to ensure the safe operation of the fluid system. For example, one or more valves may be intentionally or inadvertently repositioned during maintenance or other temporary operations, and the accurate repositioning of the valves may be necessary to ensure safe operation of the fluid system when the maintenance or temporary operations are complete.
As a specific example, modern trains often include air-operated brakes for each railcar. Pipe segments supply compressed air to each railcar along the length of the train, and each pipe segment includes an isolation valve at each end to alternately permit or prevent airflow through the pipe segment. The isolation valve is normally open when the railcar is in service to allow the compressed air to freely flow to each railcar in the train. Conversely, the isolation valve is normally shut when the railcar is taken out of service to prevent debris from entering the pipe segments.
Accidental or inadvertent repositioning of the isolation valve may prevent the air-operated brakes from working properly. For example, an isolation valve that is accidentally or inadvertently shut will prevent compressed air from being supplied to any railcars downstream from the shut isolation valve. Conversely, an isolation valve that is accidentally or inadvertently opened may allow debris to foul the pipe segment. As a result, a valve having additional safety features to lock the position of the valve and/or bias the valve to a particular position would be useful.